﻿164 
  ANNUAL 
  EEPOET 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  solid, 
  surely 
  it 
  would 
  present 
  some 
  visible 
  markings, 
  and 
  Venus 
  

   never 
  does. 
  Accordinoiy, 
  it 
  is 
  supposed 
  that 
  the 
  clouds 
  of 
  Venus 
  are 
  

   of 
  the 
  high-level 
  cirrus 
  type, 
  and 
  that 
  water-vapor, 
  though 
  present 
  

   plentifully 
  below 
  the 
  clouds, 
  is 
  too 
  scanty 
  at 
  higher 
  levels 
  to 
  be 
  

   revealed. 
  As 
  for 
  oxygen, 
  though 
  certainly 
  it 
  can 
  not 
  extend 
  as 
  high 
  

   as 
  it 
  does 
  above 
  the 
  earth, 
  it 
  may 
  be 
  present 
  beneath 
  the 
  cloud 
  level. 
  

  

  No 
  spectroscopic 
  evidence 
  of 
  the 
  rotation 
  of 
  Venus 
  has 
  ever 
  been 
  

   found. 
  This 
  proves 
  that 
  the 
  planet 
  does 
  not 
  rotate 
  very 
  rapidly, 
  like 
  

   the 
  earth 
  or 
  Mars. 
  It 
  has 
  even 
  been 
  suggested 
  that, 
  like 
  the 
  moon, 
  its 
  

   rotation 
  and 
  revolution 
  periods 
  are 
  identical 
  so 
  that 
  Venus 
  would 
  

   present 
  the 
  same 
  face 
  to 
  the 
  sun 
  at 
  all 
  times. 
  If 
  that 
  were 
  so, 
  

   the 
  bright 
  face 
  would 
  be 
  very 
  hot, 
  and 
  the 
  dark 
  face 
  very 
  cold. 
  

   Recently, 
  however, 
  Pettit 
  and 
  Nicholson 
  have 
  found 
  that 
  the 
  dark 
  

   side 
  of 
  Venus 
  is 
  about 
  equally 
  warm 
  from 
  one 
  edge 
  to 
  the 
  other 
  and 
  

   is 
  everywhere 
  at 
  about 
  the 
  same 
  temperature 
  that 
  our 
  earth 
  would 
  

   appear 
  if 
  viewed 
  from 
  another 
  planet. 
  This 
  observation 
  of 
  moderate 
  

   and 
  equable 
  night 
  temperatures 
  proves 
  that 
  the 
  planetary 
  rotation 
  

   must 
  be 
  fairly 
  rapid, 
  and 
  certainly 
  not 
  of 
  the 
  same 
  period 
  as 
  the 
  

   revolution. 
  We 
  iiuiy 
  therefore 
  conclude 
  that 
  Venus 
  is 
  very 
  prohably 
  

   appropriately 
  provided 
  with 
  temperature^ 
  humidity 
  and 
  atmospheric 
  

   conditions^ 
  and 
  is 
  in 
  a 
  state 
  suited 
  for 
  luxuriant 
  life. 
  Being 
  lohoUy 
  

   vloudy^ 
  however^ 
  it 
  is 
  douhtful 
  if 
  we 
  can 
  ever 
  demonstrate 
  it. 
  

  

  The 
  earth., 
  therefore., 
  still 
  remains 
  the 
  only 
  known 
  ahode 
  of 
  life, 
  

   and 
  her 
  life 
  depends 
  absolutely 
  on 
  the 
  suih^s 
  radiation. 
  Recent 
  

   studies 
  have 
  shown 
  that 
  this 
  dependence 
  rests 
  on 
  very 
  narrow 
  mar- 
  

   gins 
  of 
  safety. 
  For 
  instance, 
  the 
  oxygen 
  of 
  the 
  upper 
  atmosphere 
  

   is 
  induced 
  to 
  combine 
  into 
  the 
  form 
  of 
  ozone 
  by 
  the 
  influence 
  of 
  

   extreme 
  ultra-violet 
  solar 
  rays, 
  and 
  yet 
  the 
  ozone 
  formed 
  is 
  con- 
  

   tinually 
  being 
  reconverted 
  into 
  oxygen 
  by 
  the 
  influence 
  of 
  still 
  other 
  

   extreme 
  ultra-violet 
  solar 
  rays. 
  Thus 
  occurs 
  a 
  balance 
  of 
  these 
  

   effects 
  such 
  that 
  the 
  upper 
  atmosphere 
  contains 
  so 
  minute 
  a 
  quan- 
  

   tity 
  of 
  ozone 
  as 
  would 
  make, 
  if 
  brought 
  to 
  earth, 
  a 
  gaseous 
  layer 
  

   only 
  as 
  thick 
  as 
  a 
  cardboard. 
  Yet 
  this 
  minute 
  and 
  almost 
  fortuitous 
  

   atmospheric 
  constituent 
  cuts 
  off 
  entirely 
  the 
  spectrum 
  of 
  the 
  sun 
  

   and 
  stars 
  beyond 
  wave 
  length 
  2,900 
  Angstroms. 
  The 
  solar 
  rays 
  thus 
  

   cut 
  off, 
  if 
  they 
  reached 
  the 
  earth, 
  would 
  destroy 
  human 
  sight 
  and 
  

   tissues 
  by 
  their 
  powerful 
  chemical 
  activity. 
  Of 
  course, 
  we 
  could 
  

   shield 
  ourselves 
  from 
  these 
  effects, 
  but 
  our 
  ancestors 
  who 
  lived 
  before 
  

   the 
  invention 
  of 
  spectacles 
  would 
  have 
  lost 
  their 
  sight, 
  or 
  never 
  

   attained 
  it. 
  Yet 
  if 
  the 
  atmospheric 
  ozone 
  absorption 
  reached 
  only 
  

   a 
  little 
  further, 
  to 
  3,200 
  Angstroms, 
  human 
  and 
  animal 
  young 
  would 
  

   languish 
  with 
  the 
  enfeebling 
  disease 
  of 
  rickets, 
  for 
  the 
  extreme 
  

   ultra-violet 
  rays 
  are 
  indispensable 
  to 
  proper 
  mammalian 
  growth. 
  

  

  